This disclosure relates in general to process control and, more particularly, to techniques for advanced process control.
There are a variety of applications in which processes are carried out under advanced process control (APC). One model for APC is commonly known as analysis of covariance (ANCOVA), and involves a generally linear model with a continuous outcome that is a function of one or more inputs. One example of a specific application for this type of APC is control of equipment used for semiconductor fabrication, such as an etching tool that carries out an etching process on a semiconductor wafer.
In some applications involving multiple inputs for the APC, the inputs may be complex, and may even influence and/or interfere with each other, which can degrade the APC performance. Sometimes, the presence and/or effect of the interaction between inputs is identified and quantified by a human such as an engineer, which can potentially lead to unstable control performance. Consequently, although existing APC techniques have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects.